The present invention proceeds from a machine having the features defined in the preamble of claim 1. A machine of this kind has been known from DE-A-39 37 900. The known machines serve for sealing an insulating glass pane with an adhesive and sealing compound consisting of two constituents (main constituent and secondary constituent). Each of the two constituents is conveyed by a separate pump from a barrel into an intermediate storage chamber. The intermediate storage chambers are designed as piston pumps and supply gear pumps that convey the constituents to a static mixer with a nozzle provided on its end. An arrangement comprising even two successive gear pumps is provided for the main constituent. The arrangements, consisting of piston pumps and gear pumps, are stationary and connected via heated pressure hoses and heated articulated pipes with the mixer and nozzle arrangement, which latter travels along the edge of an insulating glass pane for sealing the latter. The lines cause a considerable pressure loss to occur and require extreme pressures of up to 400 bar at the pump outlets, due to the high viscosity (250-400 Pa). This entails further disadvantages: Extension of the lines and the compressibility of the compounds to be conveyed lead to metering inaccuracies; structural parts that are exposed to the compound flow are subject to increased wear; the same is true for the gear pumps and even can be drastically aggravated in the case of two-component adhesives with abrasive fillers, as normally used for sealing insulating glass panes, which may result in insufficient service life.
In order to circumvent the described wear on gear pumps, it has been known to use piston pumps for metering two-component adhesive and sealing compounds for sealing insulating glass panes (DE-A-37 03 929), in which case the pumps are supplied from an intermediate storage chamber, being in its turn supplied by a barrel pump from the respective reservoir (barrel) of the respective constituent. Here again, the hydraulically driven piston pumps are stationary and supply the mixer and nozzle arrangement via heated pressure hoses and heated articulated pipes, with the disadvantages for the metering accuracy described before. The arrangement comprising the piston pumps, intermediate storage chambers and the hydraulic drives weighs approximately 600 Kg. and cannot possibly be moved together with the nozzle.
From DE-A-39 13 000 it has been known to arrange a buffer vessel for a high-viscosity, paste-like, compressible substance near a nozzle which is supplied with that substance from the buffer vessel. However, metering of the substance is pressure-controlled, not volumetric, by subjecting the substance--which is conveyed to the nozzle through the buffer vessel by means of a stationary piston pump, for example--to a constant controlled pressure in the buffer vessel, for which purpose a pressure sensor, being part of a pressure control loop, is required in the area between the buffer vessel and the nozzle. It is a disadvantage of this system that any variation in the composition of the substance, the temperature or the viscosity, the degree of cross-linking of two constituent mixtures, etc., lead to metering inaccuracies immanent to any pressure-controlled metering system.
EP-0 709 144 A1 discloses a device having the features of the preamble of claim 1 where the intermediate storage chamber for the respective constituent is formed by a vessel, which is divided by a membrane into two chambers one of which serves to accommodate the respective constituent while the other can be supplied with a hydraulic fluid via a hydraulic pump, acting as volumetric metering pump, so that the hydraulic fluid in the vessel displaces a corresponding quantity of the respective constituent of the sealing compound. The two separate intermediate storage chambers, intended for the two constituents of the sealing compound, are supplied with the hydraulic liquid by one and the same hydraulic pump, via separately driven proportional valves. It is a disadvantage of this known device that the control valves are not capable of effecting the rapid changes in the delivery rate of the sealing compound with the necessary accuracy and the required speed. Another problem lies in the fact that the required high extrusion pressure is difficult to maintain at low delivery rates (EP 0 445 101 B1).
FR-2.597.025 A describes a device for applying a strand of a single-component adhesive on a workpiece having a piston pump which is driven by a motor via a spindle drive. A pressure sensor is provided on the cylinder of the piston pump in the area before its chamber. In order to control the quantity of adhesive exiting the nozzle, the motor speed is adjusted to the desired value via suitable control means in the case of FR-2.597.025 A.
Further disadvantages of the devices known from EP 0 709 144 and DE-37 03 929 A1 are seen in the fact that the hydraulic unit driving the metering pumps must be permanently active during operation of the devices so that energy is consumed, heat is generated and noise is developed even during times where no insulating glass panes are sealed. In addition, the quantity of the constituents present before the respective feeding member of the metering pumps (the piston in the case of a piston pump or the membrane in the reservoir according to EP 0 709 144 A1) is variable so that the marginal conditions for the metering process and the metering accuracy depend on the momentary quantity of the constituents present between the nozzle and the feeding member, which is a disadvantage especially in connection with the higher-viscosity main constituent as the latter typically accounts for approximately 90% of the sealing compound and, on top of everything, is thixotropic when a thiokol is used as sealing compound, as is usually the case.